Reusable warmers employing a super-cooled aqueous solution and an activator have been used by sportsmen and others for years to warm parts of the human body. Such a reusable warmer is shown, for example, in U.S. Pat. No. 4,077,390 to Stanley et al. (issued Mar. 7, 1978) generally at FIG. 1 and described generally at column 1, line 59 to column 2 line 4 as being a sealed bag-like flexible receptacle (such as polyethylene, nylon and the like) containing a super-cooled aqueous sodium acetate and an activator comprising a flexible metal strip having one or more slits or fissures, said patent being incorporated herein by reference. A reusable warmer having another type of activator is described in U.S. Pat. No. 4,872,442 to Manker (issued Oct. 10, 1989), said patent being incorporated herein by reference.
In reusable warmers of the present type, a supercooled solution, such as an aqueous sodium acetate solution, is contained in a flexible receptacle, such as a bag-like receptacle. The solution is activated by flexing or bending the activator strip. Upon activation, the sodium acetate in the super-cooled solution crystallizes and heat (i.e. the "heat of crystallization") is evolved. All references herein to reusable warmer or heat packs are meant to refer to the aforementioned type of heat pack in which a supercooled solution is provided in a flexible container, which also houses a trigger or activator for initiating crystallization.
One of the primary uses for such reusable warmers is the application of heat directly to various parts of the human body for therapeutic purposes such as to relieve muscle aches and pains, to reduce inflammation and to promote healing of damaged tissue. Other uses include those by sports participants (such as hunters, skiers and the like) or sports enthusiasts (such as spectators at sporting events) who use the warmers to keep various parts of their bodies warm during cold weather.
Unfortunately, because the supercooled solution used in the warmer is water-like in consistency, it is easily drawn by gravity. The resultant flowing of the solution presents a practical problem in applying the warmer to the human body. A person using a reusable warmer may be standing, sitting or walking, while trying to apply the warmer. The gravitational pull on the fluid, however, causes the solution to flow to the lowest possible point, making application difficult, if not impossible under such conditions.
Further, because the human body, in general, is contoured and not flat, attempts to apply the present-day warmers to areas such as the knee, even when the patient is in a horizontal position, present great difficulty. Because some portion of the region to be treated always will remain in a nonhorizontal position (i.e. not flat), the liquid naturally flows away therefrom.
In particular, it has been found that during use the super-cooled aqueous solution in the present-day, reusable warmers the supercooled liquid in the plastic bag will flow, for example, around a leg or arm or knee, from areas in the bag having too much solution, leaving other areas with too little. This phenomenon has been referred to as "saddlebagging."
Saddlebagging leads to uneven coverage by the reusable warmer of the body part area to be heated. Heretofore, the art has attempted to minimize saddlebagging by various means. These have included, for example, adding welds to the flexible, sealed container of the warmer so that the solution is restrained from freely flowing. Also, the use of very heavy gauge plastics which will not only be more resistant to bending, but will also act to restrain flow of the super-cooled solution and keep a more flat surface have been tried.
None of the aforementioned solutions to the saddlebagging problem has proven satisfactory, since they render the reusable warmer less comfortable and more difficult to use. Users of the reusable warmers prefer relatively flexible containers made of relatively thin materials such as polyethylene and nylon (i.e., low cost, non vinyl packages). The more flexible the warmer, the better the contact between the warmer and the body part to be treated; however, when such thin materials are used, the super-cooled solution migrates even more, further accentuating the problem of saddlebagging.
The saddlebagging problem cannot be readily solved by conventional means, as, for example, by weld placement. Adding welds also results in a less flexible and more expensive product.
A need therefore exists for a reusable warmer of the supercooled-solution type, which eliminates or minimizes saddlebagging.
The prior art warmers also suffer from another substantial problem. Although present-day, reusable warmers tend to saddlebag while unactivated, once the super-cooled solution is activated and crystallization proceeds, the converse problem is presented. During the period from activation, through crystallization, to final cooling, present-day, reusable-warmers go through a transition from water-like consistency to that of a hard, solid lump. As the phase transition proceeds, the reusable warmer becomes more and more inflexible and difficult to shape or maintain in other than a flat configuration.
The phenomenon of hardening during the heat cycle makes it extremely difficult to maintain present-day heat packs in contact with, for example, a part of the human body such as an ankle, which is not flat. Of course, if the heat pack does not stay in contact with the region to be treated, it is of no use.
From the foregoing it is clear that a need exists for a reusable warmer of the supercooled solution-type, that maintains a substantial degree of flexibility during its useful heat cycle.
Yet another problem associated with the present-day, reusable warmers of the supercooled solution-type is that their heat is generated over a fairly short period of time after activation. Accordingly, an abrupt increase to a peak temperature is reached within only a very few minutes after activation. The warmer then immediately thereafter begins an abrupt decline in temperature. For the user, this translates into a high initial temperature followed by a cooling in a short period of time to a temperature less than desired for treating the afflicted area.
The problem, then, with the prior art warmers is that they reach a peak temperature abruptly and then immediately begin to cool quickly. A need therefore exists for a reusable warmer of the supercooled solution type having a more sustained period of time during which the heat pack remains within a therapeutically useful temperature range.